1. Field of the Invention
The present invention relates to a processing solution preparation and supply method and apparatus and, more particularly, to a method of preparing a processing solution for use in processing of a substrate on which an element is to be formed, and supplying the prepared processing solution to the substrate processing step, and an apparatus for the method.
2. Related Background Art
Generally, to form elements on a substrate in, e.g., the fabrication process of a semiconductor device such as a memory or logic circuit or of a liquid crystal display, the fabrication process of a flat panel display, or the fabrication process of a multilayered printed circuit board, thin films such as an insulator layer, semiconductor layer, and conductor layer are first sequentially formed on the surface of the substrate.
Subsequently, after the uppermost one of these thin films is coated with a resist layer, exposure is performed using a photomask, and patterning is performed using a resist developer. The resist pattern obtained by the development is used as a protective film to pattern the underlying thin films by etching by using an etchant. After that, the resist remaining on the substrate surface is removed by a resist stripper.
Also, before and after these processes, fine particles, foreign matter, and the like sticking to the substrate surface are removed by a cleaner. These series of photolithography steps are repeated in accordance with the number of photomasks. So, large amounts of the processing solutions such as the developer, etchant, resist stripper, and cleaner are used.
On the other hand, metal wiring layers for connecting components in each element and interconnecting elements are formed on the substrate. Copper lines which will be used most often in the future are formed by plating. In this plating, a substrate is dipped (immersed) in a plating bath having a copper electrode which also replenishes copper ion, and electrodeposition is performed by circulating a copper plating solution as a processing solution.
The amounts of the processing solutions used in the photolithography and plating as described above have significantly increased with a recent increase in size and mass-production of substrates.
Of these processing solutions, the composition and concentration of each photolithography processing solution must be strictly controlled in order to obtain high resolution, high patterning accuracy and precision, high stability, and high yield in accordance with the corresponding processing step. In particular, with the recent increasing density of patterning, the patterning width is required to be decreased.
For example, line widths of 0.1 μm level, 1 μm level, and 10 μm level are desired for a semiconductor substrate, liquid crystal substrate, and multilayered printed circuit board, respectively. Furthermore, a small line width of 1 μm or less is demanded to incorporate a semiconductor circuit on a liquid crystal substrate by the low-temperature polysilicon TFT technology. To achieve this small line width, the concentration variation of the photolithography processing solution must be controlled to ± 1/1,000 or less of the target concentration.
In addition, to minimize patterning defects, a so-called particle content of the photolithography processing solution must be very small. For example, strict limitations are required by which the number of particles of 0.1 μm or more is 10 or less, or 1 or less in some cases, in 1 ml of the photolithography processing solution. Such particle control conditions similarly apply to the plating solution described above.
Conventionally, each processing solution is exclusively prepared by a processing solution manufacturer (to be referred to as a “supply side” hereinafter) by dissolving a material powder in pure water to prepare an undiluted solution, adjusting the concentration by diluting this undiluted solution, and filtering out particles by microfiltration. This processing solution is filled in a vessel and supplied to a substrate processing place (to be referred to as a “use side” hereinafter) such as a semiconductor fabrication plant, liquid crystal substrate fabrication plant, or multilayered printed circuit board fabrication plant.
This is so because the installation cost and operation cost increase if the processing solution is prepared by dissolving a solid material in the form of a crystal powder or grains and adjusting the composition and concentration on-site in the semiconductor fabrication plant, liquid crystal substrate fabrication plant, or the like.
Additionally, it is extremely difficult to well control handling of the material powder and the like, dilution of the undiluted solution, and the composition and concentration. Also, the solid material itself in the form of a powder or the like produces particles, so the use of the solid material is essentially disliked. This tendency is particularly notable if the solid material contains a metal. Under these circumstances, no processing solution is currently prepared from a solid material on-site in a semiconductor fabrication plant, liquid crystal substrate fabrication plant, or the like.
Furthermore, the concentration of, e.g., the photolithography processing solution largely changes in accordance with the type, application, or the like of the processing solution. On the supply side, the concentration is usually adjusted to 0.1 to 5 mass %.
More specifically, an aqueous oxalic acid solution used as an etchant for a transparent conductive film in the liquid crystal substrate fabrication process is most often an aqueous solution having an oxalic acid concentration of 3.5 mass %. An aqueous potassium hydroxide solution used as an STN developer in the liquid crystal substrate fabrication process is most often an aqueous solution having a potassium hydroxide concentration of 0.7 mass %.
Also, an aqueous sodium hydroxide solution used as a developer in the printed circuit board fabrication process is most often an aqueous solution having a sodium hydroxide concentration of 1.0 mass %. Furthermore, an aqueous sodium hydroxide solution used as a resist stripper in the printed circuit board fabrication process is most often an aqueous solution having a sodium hydroxide concentration of 5.0 mass %.